An organic electronic device such as an organic light emitting diode (“OLED”) (the OLED can be used in, for example, a display or as a light source element of a light source), an organic light sensor, an organic transistor, an organic solar cell, or an organic laser require protection from oxygen and moisture in the atmosphere, and therefore employ some form of encapsulation. One common procedure to encapsulate the organic electronic device is to sandwich it between a substrate and an encapsulation lid, and an adhesive around the perimeter of the device holds together the substrate and the encapsulation lid such that there is a continuous perimeter seal around the device.
OLEDs, in general, are known in the art and are discussed in, for example, U.S. Pat. No. 5,457,565 entitled “Organic Electroluminescent Device”. Organic light sensors, in general, are also known in the art and are discussed in, for example, U.S. Pat. No. 6,483,099 entitled “Organic Diodes with Switchable Photosensitivity”. Organic transistors, in general, are known in the art and are discussed in, for example, U.S. Pat. No. 6,485,884 entitled “Method for Patterning Oriented Materials for Organic Electronic Displays and Devices.” Organic solar cells are also known in the art and are discussed in, for example, U.S. Pat. No. 4,963,196 entitled “Organic Solar Cell”. Organic lasers are known in the art and are discussed in, for example, U.S. Pat. No. 5,881,089 entitled “Article Comprising an Organic Laser”.
When manufacturing an organic electronic device, adhesives that provide low total accumulated cycle (“TAC”) times and that remain stable or are workable over extended periods of time are desirable. Thermal-cure adhesives can be used to manufacture the organic electronic device but they have long TAC times (e.g., thermal-cure adhesives typically take an hour to cure) and is workable for only a short time (e.g., once the resin is mixed, the thermal-cure adhesive will typically cure after an hour or even less and the curing can occur anywhere, even in the dispensing equipment). On the other hand, UV-curable adhesives can cure very quickly when exposed to UV radiation (e.g., UV-curable adhesives have a low TAC time typically about ninety seconds), yet remain stable or workable for long periods until triggered by the UV radiation at a user-designated point in the process sequence. These characteristics, among others, make it desirable to use UV-curable adhesives to form the perimeter seal to encapsulate the organic electronic device.
In terms of degradation caused by the environment, the electronic device's lifetime is related to the permeation rate of oxygen and particularly water across this perimeter seal (the permeation rate through the substrates is generally negligible). This permeation rate is a sum of the permeation through the bulk of the sealing material (“bulk diffusion”) and permeation along the interfaces between the sealing material and the substrate or encapsulation lid (“interface diffusion”). When the bonding to the encapsulation lid is weak (i.e., there's poor adhesion), permeation along this interface can be high, greatly shortening the device lifetime. Furthermore, poor adhesion can lead to delamination during mechanical processes such as scribe and break (i.e., device singulation). Therefore, strong adhesion to the encapsulation lid is important to effectively encapsulate the elements.
FIG. 1 shows a prior art encapsulated organic electronic device 106. In FIG. 1, an organic electronic device 115 is fabricated on a substrate 118. As stated earlier, the organic electronic device 115 can be an OLED, an organic light sensor, an organic transistor, an organic solar cell, or an organic laser. A UV-curable adhesive 112 is applied around the perimeter of the organic electronic device 115. An encapsulation lid 109 is placed on the UV-curable adhesive 112 in order to encapsulate the organic electronic device 115. The encapsulation lid 109 is nonopaque. The substrate 118 and the encapsulation lid 109 are moved together so that the UV-curable adhesive 112 is in contact with both the substrate 118 and the encapsulation lid 109. Then, UV radiation is applied to the UV-curable adhesive 112 in order to cure it (e.g., the adhesive absorbs the UV-radiation and transfers that energy to cross-link the adhesive groups so that the adhesive becomes rigid). One of the disadvantages of this configuration is that over time, delamination typically occurs at the interface between the UV-curable adhesive 112 and the encapsulation lid 109.
In order to decrease the likelihood of delamination and improve adhesion, an additional adhesion layer is typically incorporated. Incorporating the adhesion layer to improve encapsulation of the organic electronic device is not effective if UV-curable adhesive is also used since the materials that are good adhesion layers typically require a thickness that makes them opaque. FIG. 2 shows the prior art use of the adhesion layer extended to organic electronic device encapsulation. In FIG. 2, an organic electronic device 115 is fabricated on a substrate 118. An opaque adhesion layer 221 is deposited on the encapsulation lid 209. A UV-curable adhesive 112 is applied on the substrate 118 around the perimeter of the organic electronic device 115, or alternatively, applied on the opaque adhesion layer 221 such that when the encapsulation lid 209, the substrate 118, and the UV-curable adhesive 112 are brought together, the organic electronic device 115 is sealed around its perimeter. After the UV-curable adhesive is applied, the substrate 118 and the encapsulation lid 209 are moved together so that the UV-curable adhesive 112 is in contact with both the substrate 118 and the opaque adhesion layer 221 to seal the organic electronic device. Because this adhesion layer is opaque, UV radiation will not reach the UV-curable adhesive 112 to cure that adhesive. Therefore, one of the disadvantages of this configuration is that UV-curable adhesive cannot be used. A thermal-cure adhesive can be used, but this adhesive results in high TAC times and is workable for only a short time.
For the foregoing reasons, there exists a need to encapsulate the organic electronic device using a UV-curable adhesive such that there is strong adhesion at the interface between the UV-curable adhesive and the encapsulation lid.